Converts ash to use aura-mus

ash/mus/native_widget_factory_mus.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef ASH_MUS_NATIVE_WIDGET_FACTORY_MUS_H_
-#define ASH_MUS_NATIVE_WIDGET_FACTORY_MUS_H_
-
-#include "base/macros.h"
-
-namespace ash {
-namespace mus {
-
-class WindowManager;
-
-// A native widget factory used for widgets in the ash system UI itself.
-// For example, this creates context menu widgets for the shelf and wallpaper.
-class NativeWidgetFactoryMus {
- public:
-  explicit NativeWidgetFactoryMus(WindowManager* window_manager);
-  ~NativeWidgetFactoryMus();
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(NativeWidgetFactoryMus);
-};
-
-}  // namespace mus
-}  // namespace ash
-
-#endif  // ASH_MUS_NATIVE_WIDGET_FACTORY_MUS_H_